Small animal imaging is an important field of research in many areas including preclinical pharmaceutical development, developmental biology, cardiac research, and molecular biology. Several small animal models are widely used in these fields, the most prevalent being the mouse and the rat. High frequency ultrasound has been widely used to image the mouse model at frequencies from about 20 megahertz (MHz) to over 60 MHz. The rat model, however, is difficult to image at high frequencies in comparison to the mouse because the rat has highly attenuating and echogenic epidermal, dermal, and sub-dermal tissues.